The first version of this entry was created in April 2000.
It was based on data summarized in
(1) H. S. P. Müller, T. Klaus, and G. Winnewisser,
2000, Astron. Astrophys.357, L65.
The second entry from Aug. 2009 was based on new
rest frequencies for the N = 1  0
and 2  1 transitions obtained from astronomical
observations described in
(2) M. Padovani, C. M. Walmsley, M. Tafalla, D. Galli,
and H. S. P. Müller,
2009, Astron. Astrophys.505, 1199.Note: Previously
used, seemingly more accurate data show considerable
off-sets; see (2) for further details.
Besides these data and the submillimeter data from (1),
frequencies for the N = 3  2 transition
were taken from
(3) K. V. L. N. Sastry, P. Helminger, A. Charo,
E. Herbst, and F. C. DeLucia,
1981, Astrophys. J.251, L119.
The third, present entry combines rotational and
rovibrational data of several low-lying states.
Ground state transitions were taken from the original data
in (13). The effect of the additional data on
the ground state data is negligible.
The v2 = 1 rotational
lines were taken from
(4) D. R. Woodward, J. C. Pearson, C. A. Gottlieb,
M. Guélin, and P. Thaddeus,
1987, Astron. Astrophys.186, L14.
Data for v2 = 2,
v3 = 1, and for
v2 = v3 = 1
were published in
(5) T. C. Killian, C. A. Gottlieb, and P. Thaddeus,
2007, J. Chem. Phys.127, Art. No. 114320.
ν3 infrared transitions were measured
by
(6) H. Kanamori, K. Seki, and E. Hirota,
1987, J. Chem. Phys.87, 73.
Data for the ν2 + ν3
band were given in
(7) K. Kawaguchi, T. Amano, and E. Hirota,
1988, J. Mol. Spectrosc.131, 58.
Transitions for 5ν2 and the hot bands
5ν2  ν2 and
ν2 + ν3
 ν2 were published
by
(8) H. Kanamori and E. Hirota,
1988, J. Chem. Phys.89, 3962.
Additional spectroscopic parameters of states
up to 2200 cm1 were taken
from
(9) Y.-C. Hsu, J.-M. Lin, D. Papoušek, and J.-J. Tsai,
1993, J. Chem. Phys.98, 6690;
(10) Y.-C. Hsu, Y.-J. Shiu, and C.-M. Lin,
1995, J. Chem. Phys.103, 5919;
(11) W.-Y. Chiang, Y.-C. Hsu,
1999, J. Chem. Phys.111, 1454;
or have been estimated from these data.
NOTE:
The anharmonic interaction between
v2 = v3 = 1
and v2 = 5 can only be
accounted for approximately using simple assumptions
and has thus been ignored as in (8). As hyperfine
structure data are available for some states it has been
ignored in the energy file. This leads to small differences
for the partition function values which can be neglected.
Different l-components of a given vibrational state
have been treated separately but will appear in the same
entry as far as appropriate. Partition function values
for only the ground vibrational state are given in
parentheses. The partition function values
are reliable up to 300 K, quite reasonable up to
500 K, and should be viewed with great caution at
higher temperatures.
Predictions should be viewed with increasing caution
above 1.5 THz or N > 17.
The dipole moment is from an ab initio
calculation by
(12) D. E. Woon,
1995, Chem. Phys. Lett.244, 45.
It is assumed that vibrational changes are negligible;
this may be incorrect. Transition dipole moments
were estimated from calculated infrared intensities
published by
(13) R. Tarroni and S. Carter,
2004, Mol. Phys.102, 2167.